Gas turbine engines include compressor blades that rotate to compress inlet gases and turbine blades that rotate to harness energy from expansion of outlet gases. Gas turbine blades are attached to gas turbine disks. The gas turbine disks rotate with the gas turbine blades and may experience peak stresses in excess of about 1000 megapascals (MPa) due to centrifugal loading from the gas turbine blades and weight of the gas turbine disks themselves.
In some examples, gas turbine disks may not be directly exposed to the flow path of hot gases in the gas turbine engine. Thus, in some implementations, maximum surface temperatures of the gas turbine disks may be about 650° C. The thermal and mechanical stresses to which the gas turbine disks are exposed impose design criteria which the alloys that form the gas turbine disks may satisfy. These design criteria include relatively high yield strength and tensile strength to inhibit yield and fracture of the gas turbine disk, relatively high ductility and fracture toughness to impart tolerance to defects, relatively high resistance to initiation of fatigue cracks, and relatively low fatigue crack propagation rates. In some implementations, gas turbine disks may be formed from nickel (Ni)-based superalloys, which may satisfy at least some of these design criteria.
In some examples, compressor blades may be an integral part of the gas turbine disk. In such cases, separately bladed and integrally bladed gas turbine disks may experience similar operating temperatures and thermal and mechanical stresses, and, thus, may have similar material design criteria.
As operating temperatures of gas turbine engines increase in search of greater operating efficiency, surface temperatures of the gas turbine disk may increase. As maximum surface temperatures of the gas turbine disk increase above 700° C., oxidation and/or hot-corrosion of the surface of the gas turbine disk may become more likely. Oxidation or hot corrosion may change the chemical composition, phase constitution, and/or resulting microstructure of the surface region of the gas turbine disk. This may affect the resulting mechanical properties of the gas turbine disk, as the mechanical properties may be affected by the chemical composition, phase constitution, and microstructure of the alloy. Thus, is some examples, a gas turbine disk includes a coating that provides oxidation- and/or hot-corrosion-resistance to the surface of the gas turbine disk.